At least half of all new HIV infections in the United States occur among people under age 25. Moreover, substance use increases risk for HIV and other potential negative outcomes. Youth living in impoverished areas with high rates of HIV and substance abuse are significantly more vulnerable than their peers in the general population. Published HIV-prevention interventions have demonstrated some effectiveness at reducing risky sexual and substance use behaviors, but their effects have generally been limited. Incorporating social-level factors in prevention interventions has potential to improve both efficacy and longevity of these efforts. It is well established that sexual behavior and substance use are influenced by peer behavior and norms. However, little research has examined how romantic relationships, a normative outgrowth of peer relationships, affect these risk behaviors. The goal of this project, therefore, is to explore the role of these romantic relationships among urban youth at risk (ages 16-20) who are sexually active and using substances. This exploratory project will use multiple methods of data collection to address three aims: to (1) identify and explore factors at the individual and dyadic levels that influence sexual behavior placing youth at risk for sexually transmitted infections including HIV; (2) identify and explore factors at the individual and dyadic levels that influence substance use, including as they relate to sexual risk behavior; and (3) develop a brief, HIV-prevention intervention for adolescent couples, in order to a) determine the acceptability and feasibility of delivering a program in this format, and b) pilot test the specific components of the intervention. The project is guided by Social Cognitive and Attachment theories. It will consist of three main phases: a formative research phase, including focus groups for youth, parents, and service providers; a survey; and an adaptation of a validated videotaped interaction task with adolescent couples; a development phase, in which we will create a brief couples intervention; and a components testing phase, where we test the draft intervention, and gather feedback about its content, acceptability, and feasibility. A better understanding of dyadic issues as they relate to substance use and sexual risk behavior among vulnerable adolescents has great potential to improve intervention efforts for youth at risk for HIV.